The chemistry of this crucial process is surprisingly simple and common. It is based on the electric polarity of water. Because of this polarity, certain molecules are hydrophilic (attracted by water), while others are hydrophobic (repelled by water). A third kind of molecules are those of fatty and oily substances, known as lipids. They are elongated carbon structures with one hydrophilic and one hydrophobic end. (See Picture)

When these lipids come in contact with water, they spontaneously form various structures. For example, they may form a mono-molecular film spreading over the water surface or alternatively they may form an even more complex double layer of molecules with water on both sides, as shown in the Picture. These single or double layers can form droplets, which are the membrane-bounded vesicles. These double-layered greasy membranes show a surprising number of properties similar to contemporary cellular membranes. They restrict the number of molecules that can enter the vesicle, transform solar energy into electrical energy and even collect phosphate compounds inside their structure.